1. Field of the Invention
This invention relates to a dust seal assembly for closed type mixer, its control mechanism.
2. Description of the Prior Art
The dust seal assemblies which have thus far been accepted for use in the art are described, for example, in Japanese Patent Publication No. 49-27895 and Japanese Patent Publication No. 46-27117.
More specifically, the former publication describes a dust seal for a mixer, which is constituted by a floating ring interposed between an end plate and a rotor, and a wear ring with a separately formed facing, assembling the floating ring and facing through sliding surfaces of a material which can endure sliding action in a non-lubricated or almost non-lubricated state. The wear ring is supplied with a temperature adjusting fluid and provided with an outlet for discharging an internally stagnant material. This dust seal has a sufficiently long service life without lubrication or with a slight degree of lubrication.
The former publication sets forth a disclosure with regard to application of lubricant oil to the sliding surfaces of the floating ring and facing, but contains no indications concerning the timing of oiling or particular means of lubrication. That is to say, such focuses on minimize of oil consumption but gives no considerations to the degree or condition of mixing which is very important. In addition, such publication gives no consideration to the utilization of seal surface control means.
In the second publication, arrangements are disclosed to operate a dust seal yoke by a controllable hydraulic pressure transmission for the purpose of controlling the sealing pressure. Although a pressure regulator valve is provided in its hydraulic circuit, it is operated regardless of the degree of mixing.
As is known in the art, the load of a mixer varies from time to time in the initial and final stages of a mixing operation, as a result varying the sealing surface pressure and temperature. Therefore, it is difficult to secure the desired functions of a dust seal assembly by supplying oil or controlling the sealing pressure regardless of these variations.
Moreover, actually used mixers require the replacement of wornout parts. On such occasions, it is difficult to replace movable component parts although replacement of parts on the fixed side is relatively easy.